Fuel cut control method

ABSTRACT

To provide a fuel cutoff control method for an engine including a secondary air introducing system, capable of preventing afterburning in an exhaust pipe at the time of fuel being cut off in a decelerating state of the engine.  
     A fuel cutoff control method during deceleration of an engine including a secondary air introducing pipe connected to an exhaust pipe, and an air cut valve provided on the secondary air introducing pipe, the method comprising a determination step of determining under predetermined conditions whether or not the engine is in a decelerating state, wherein in the decelerating state, a greater amount of fuel than a normally required amount of fuel flow is supplied during a predetermined period of time after the start of deceleration, and then fuel is cut off after the predetermined period of time has elapsed.

FIELD OF THE INVENTION

[0001] This invention relates to a fuel cutoff control method for anengine and particularly to a fuel cutoff control method duringdeceleration for an automobile engine.

TECHNICAL BACKGROUND

[0002] In a conventional motorcycle or the like with a fuel injectionengine mounted, engine operating conditions are determined based on loadand engine speed. When it has been determined to be unnecessary tosupply fuel because the engine is in a decelerating state, the supply offuel is cut off and a fuel injection amount is reduced to 0. Reducingthe fuel injection amount to 0 during deceleration provides adecelerating effect of engine braking, as well as improved fuelefficiency and cleaner exhaust gas.

[0003] Such a configuration is also used as a means for cleaning exhaustgas that a secondary air introducing pipe is connected to an exhaustpipe, and exhaust gas is recombusted with secondary air introduced tothe exhaust pipe by utilizing the pulse of exhaust gas pressure. An aircut valve is provided on the secondary air introducing pipe. The air cutvalve opens at high engine speed with the throttle opened during normaldriving or acceleration to introduce secondary air, while closing at lowengine speed with the throttle closed during deceleration to cut off thesecondary air.

[0004] In a vehicle including this type of secondary air introducingsystem, during deceleration, the supply of secondary air to the exhaustpipe is cut off, and the supply of fuel is also cut off to reduce thefuel injection amount to 0 as described above.

[0005] However, in the case that the engine shifts from a normal runningstate to a decelerating state while the throttle being closed, if fuelis cut off simultaneously with the start of deceleration, fuel adheredto an intake pipe wall flows into a cylinder immediately after fuel isstarted being cutoff. Since the adhered fuel is too lean to combustalone in the cylinder, it is exhausted into the exhaust pipe as unburnedgas. In the case of a vehicle including the secondary air introducingsystem, the unburned gas which flows into the exhaust pipe reacts withsecondary air to combust, thereby causing afterburning. The afterburningaffects the engine itself as well as causing noise.

[0006] In order to prevent the afterburning, the foregoing air cut valveis provided to cut off the supply of the secondary air when intake pipepressure has been lowered to a specified value or below.

[0007] The air cut valve, however, operates with a delay, so that evenif it is driven to be closed simultaneously with a fuel cutoff command,no afterburning can be completely prevented which occurs during an earlystage after fuel has been cut off.

[0008] In view of the foregoing, an object of this invention is toprovide a fuel cutoff control method for an engine including a secondaryair introducing system, capable of preventing afterburning in an exhaustpipe at the time of fuel being cut off in a decelerating state of theengine.

DISCLOSURE OF THE INVENTION

[0009] In order to achieve the foregoing object, the invention providesa fuel cutoff control method during deceleration of an engine includinga secondary air introducing pipe connected to an exhaust pipe, and anair cut valve provided on the secondary air introducing pipe, the methodcomprising a determination step of determining under predeterminedconditions whether or not the engine is in a decelerating state, inwhich in the decelerating state, a greater amount of fuel than anormally required amount of fuel flow is supplied during a predeterminedperiod of time after the start of deceleration, and then fuel is cut offafter the predetermined period of time has elapsed.

[0010] In this configuration, even if it has been determined that fuelbe cut off in a decelerating state of the engine, the fuel injectionamount is not immediately reduced to 0. A required amount of fuel flowcomputed according to a normal program is multiplied by an increasingcoefficient and an increased amount of injected fuel is supplied duringa predetermined period of time until the air cut valve of the secondaryair introducing pipe is closed. The fuel injection amount is reduced to0 after the predetermined period of time has elapsed and the air cutvalve has been closed. Thereby at the start of deceleration, when athrottle is closed and the fuel adhered to the intake pipe wall flowsinto the cylinder due to increased negative intake pressure, the adheredfuel completely combusts in the cylinder together with the additionalfuel injected from the injector (the adhered fuel is too lean to combustalone). Therefore, nounburned gas flows into the exhaust pipe.Afterburning caused by reaction of the unburned gas and secondary air inthe exhaust pipe is thus prevented.

[0011] Incidentally, the predetermined period of time may be set as theelapse of a predetermined time through time control or as predeterminedengine cycles in the case that fuel cutoff control judgment is made perstroke (cycle).

[0012] In a preferred embodiment, when it has been determined at thedetermination step that the engine is not in the decelerating state, ifthe engine is regaining speed back from the decelerating state, a lessamount of fuel than normally required is supplied.

[0013] In this configuration, when the engine returns to a normalrunning state back from the decelerating state while the throttle beingreopened, a required amount of fuel flow computed according to a normalprogram is multiplied by a reducing coefficient and a reduced amount ofrequired injected fuel is supplied. This prevents a sharp increase inengine speed caused by a sharp increase in the fuel injection amount andmaintains a stable running state of a vehicle.

[0014] In another preferred embodiment, the fuel cutoff control methodfurther comprises as the predetermined conditions: a step of determiningthe time elapsed since an engine start; and a step of determiningcooling water temperature.

[0015] In this configuration, an intake air amount is calculated basedon intake pipe pressure data detected as computing data at anappropriate crank angle. The intake air amount and engine speed canappropriately determine the operating conditions of the engine. Further,fuel cutoff control is prevented at an engine start and when coolingwater temperature is low so that the stable operating conditions of theengine can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows a configuration of an overall control system of amotorcycle according to the invention.

[0017]FIG. 2 is a schematic diagram of a crank angle detection devicefor an engine according to the present invention.

[0018]FIG. 3 is a flowchart of fuel cutoff control according to theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] An embodiment of the present invention will be described belowwith reference to the accompanying drawings.

[0020]FIG. 1 is a block diagram of an entire control system of amotorcycle according to the embodiment of the present invention.

[0021] An engine control unit (ECU) 1 is unitized to be an integralcomponent. A control circuit CPU (not shown) of the ECU 1 receivesinputs including an on/off signal from a main switch 2, a crank pulsesignal from a crank pulse sensor 3, an intake air pressure detectionsignal from an intake air pressure sensor 4, an intake air temperaturedetection signal from an intake air temperature sensor 5, a coolingwater temperature detection signal from a water temperature sensor 6, avoltage signal from an injector voltage sensor 7 for controlling aninjector, and a checking input signal from a switch box 8 having aplurality of switches SW1 to SW3. The ECU 1 is also connected to abattery 20, from which battery power supply is inputted.

[0022] For outputs from the ECU 1, the ECU 1 outputs a pump relay outputsignal to a pump relay 9 for driving a fuel pump, an injector outputsignal for driving an electromagnetic coil of an injector 10, anignition coil output signal for driving an ignition coil 11, an autochoke output signal for driving an auto choke 12 in response to coolingwater temperature, a diagnosis warning signal for driving a diagnosiswarning lamp 13 in a meter 22 when abnormality is detected, a watertemperature warning signal for driving a water temperature warning lamp14 to indicate a warning when the cooling water temperature exceeds agiven temperature, and an immobilizer warning signal for driving animmobilizer warning lamp 15 when an immobilizer 17 of an engine key orthe like is abnormally operated. Power supply voltage is outputted forsupplying power to each sensor either through a sensor power supplycircuit 21 or directly.

[0023] The ECU 1 is also connected to an external general-purposecommunication device 18 and capable of inputting/outputting control dataor the like through a general-purpose communication line. The ECU 1 isfurther connected to a serial communication device 19 and capable ofhandling serial communication.

[0024]FIG. 2 is a system structure diagram of a crank angle detectiondevice according to the embodiment of the present invention. Asingle-cylinder four-stroke engine 30 is formed with a combustionchamber 32 on top of a piston 31. An intake pipe 33 and an exhaust pipe34 are connected to the combustion chamber 32 so as to communicate withthe combustion chamber 32. A throttle valve 35 is provided in the intakepipe 33, and an intake valve 36 is disposed at an end thereof. Anexhaust valve 37 is provided at an end of the exhaust pipe 34. Areference numeral 38 denotes a spark plug. A cooling jacket 39 isprovided around a cylinder of the engine 30, to which the watertemperature sensor 6 is attached. The piston 31 is connected to acrankshaft 41 via a connecting rod 40.

[0025] A ring gear 42 is integrally secured to the crankshaft 41. Thering gear 42 has plural teeth (projections) 43 formed at equalintervals, among which one toothless portion 44 is provided. The crankangle sensor (crank pulse sensor) 3 is provided for detecting the teeth43 formed on the ring gear 42. The crank angle sensor 3 detects eachtooth 43 to generate a pulse signal having a pulse width thatcorresponds to a lateral length on the upper side of the tooth. In thisexample, 12 portions to be each provided with the tooth 43 include onetoothless portion 44 so that the sensor generates 11 (eleven) pulsesignals one per 30° of one crank rotation.

[0026] The injector 10 is attached to the intake pipe 33. Fuel pumpedfrom a fuel tank 45 through a filter 47 using a fuel pump 46 isdelivered to the injector 10 under a constant fuel pressure maintainedby a regulator 48. The ignition coil 11 controlled by the ECU 1 (FIG. 1)is connected to the spark plug 38. The intake air pressure sensor 4 andthe intake air temperature sensor 5 are attached to the intake pipe 33,which are separately connected to the ECU 1.

[0027] A secondary air introducing pipe 49 for cleaning exhaust gas isconnected to the exhaust pipe 34. An air cut valve 50 is provided on thesecondary air introducing pipe 49. The air cut valve 50 opens at highengine speed with the throttle opened during normal driving oracceleration to introduce secondary air, while closing at low enginespeed with the throttle closed during deceleration to cut off thesecondary air.

[0028]FIG. 3 is a flowchart of fuel cutoff control according to thepresent invention.

[0029] Step S1: Determines whether or not timing is correct for intakeair amount calculation. Since the crank angle is predetermined at whichintake pipe pressure used as an intake air amount calculation parametercan be properly detected, it is determined whether or not the timing atthe predetermined crank angle is met. When the intake valve is open, theintake pipe pressure and in-cylinder pressure become approximately equalto each other. Intake pipe pressure data, therefore, is input when it isdetermined by a crank angle signal that an intake stroke is finished,and an intake air amount is calculated based on the input data.

[0030] The crank angle is detected in such a way that each of the teethof the ring gear attached to the crankshaft is detected by the crankangle sensor, the generated crank pulse signal is input to the CPU inthe ECU, and then the crank angle is determined from the signal data.The CPU is configured to run an interrupt program every time the crankangle signal is input, and engine speed is calculated based on intervalsat which the pulse signals are inputted.

[0031] Step S2: Converts the detection data outputted from the intakeair pressure sensor from analog to digital and then reads and saves ifit is determined that the timing of the intake air amount calculation ismet.

[0032] Step S3: Calculates the intake air amount based on the intakepipe pressure data.

[0033] Step S4: Determines whether or not a specified time has elapsedafter an engine start. The elapsed time is measured here since thecrankshaft rotation was started and the first crank pulse signal wasgenerated. If the predetermined time has not yet elapsed, adetermination is made that the engine has just been started. No fuelcutoff control is performed during the engine start because warm-upcontrol is performed. If engine conditions have changed from warm-up tonormal operation after the engine start and the elapse of thepredetermined time (or if a certain time has elapsed since immediatelyafter the engine start and the engine has shifted to a stable state evenduring warm-up), the process proceeds to the next step S5.

[0034] Step S5: Determines whether or not cooling water temperature is apredetermined threshold value or above. If the engine is being warmed upat low cooling water temperatures, no fuel cutoff control is performed.Instead, a normally required amount of injected fuel is calculatedaccording to a program designed for warm-up and then supplied (stepS13).

[0035] Step S6: Determines the engine operating conditions based on theresult of a computation of engine speed and the intake air amount. Thisdetermines whether the engine is in a decelerating state or in anaccelerating state, or running at a normal, constant speed.

[0036] Step S7: Determines whether or not the engine is in adecelerating state based on the result of the determination at the stepS6.

[0037] Step S8: If the engine is in a decelerating state, it isdetermined whether or not a specified time has elapsed since the startof deceleration. The specified time is as long as the time during whichthe air cut valve of the secondary air introducing system is completelyclosed to end its operation.

[0038] Step S9: If the specified time has not yet elapsed at the stepS8, that is, when the air cut valve is still open, a required amount offuel calculated according to the engine operating conditions ismultiplied by a rich coefficient (greater than 1) to increase the amountof fuel, and then fuel injection is performed. Thereby when the throttleis closed and the fuel adhered to an intake pipe wall flows into thecylinder due to increased negative intake pressure, the adhered fuelcompletely combusts in the cylinder together with the additional fuelinjected from the injector (the adhered fuel is too lean to combustalone). Therefore, no unburned gas flows into the exhaust pipe.Afterburning caused by reaction of the unburned gas and secondary air inthe exhaust pipe is thus prevented.

[0039] Step S10: If the specified time has elapsed since the start ofdeceleration, that is, when the air cut valve of the secondary airintroducing system has been completely closed, the fuel injection amountis reduced to 0. Since the secondary air is blocked in this state, evenif the unburned gas flows into the exhaust pipe, afterburning isprevented from occurring.

[0040] Step S11: If the determination is made at the step S7 that theengine is not in a decelerating state, it is determined whether or notthe engine is regaining speed back from the decelerating state.

[0041] Step S12: If the engine is regaining speed back from thedecelerating state, a required amount of fuel calculated according tothe engine operating conditions is multiplied by a regaining coefficient(smaller than 1) to reduce the amount of fuel, and then fuel injectionis performed. This prevents a sharp increase in engine speed and allowsthe engine to smoothly shift to a normal running state from thedecelerating state.

[0042] Step S13: Injects a required amount of fuel calculated accordingto the engine operating conditions directly from the injector.

INDUSTRIAL USABILITY

[0043] In the present invention as discussed above, even if it has beendetermined that fuel be cut off in a decelerating state of the engine, afuel injection amount is not immediately reduced to 0. A required amountof fuel flow computed according to a normal program is multiplied by anincreasing coefficient to supply an increased amount of injected fueluntil the air cut valve of the secondary air introducing pipe is closed.The fuel injection amount is reduced too after the air cut valve isclosed. This allows the fuel to combust in the cylinder at the start ofdeceleration, even before the air cut valve of the secondary airintroducing pipe is closed, so that the unburned gas is prevented fromflowing into the exhaust pipe. Afterburning caused by reaction of theunburned gas and secondary air in the exhaust pipe is thus prevented.

1. A fuel cutoff control method, comprising: determining underpredetermined conditions whether or not an engine is in a deceleratingstate; supplying a greater amount of fuel than a normally requiredamount of fuel flow during a predetermined period of time after startingto decelerate; and cutting off the fuel after the predetermined periodof time has elapsed.
 2. The fuel cutoff control method according toclaim 1, further comprising supplying a less amount of fuel thannormally required when it has been determined that the engine is not inthe decelerating state, if the engine is regaining speed back from thedecelerating state.
 3. The fuel cutoff control method according to claim1, further comprising: determining a time elapsed since an engine start;and determining a cooling water temperature as the predeterminedconditions.
 4. The fuel cutoff control method according to claim 2,further comprising: determining a time elapsed since an engine start;and determining a cooling water temperature as the predeterminedconditions.
 5. The fuel cutoff method according to claim 1, furthercomprising determining whether or not to take an intake air amountcalculation.
 6. The fuel cutoff method according to claim 5, furthercomprising calculating the intake air amount based on intake pipepressure data.
 7. The fuel cutoff method according to claim 6, furthercomprising inputting the intake pipe pressure data when it is determinedthat an intake stroke has been completed.
 8. The fuel cutoff methodaccording to claim 7, further comprising converting data from an intakeair pressure sensor from analog data to digital data.
 9. The fuel cutoffmethod according to claim 8, further comprising storing the converteddata.
 10. The fuel cutoff method according to claim 9, furthercomprising saving the converted data if it is determined that a timingof the intake air amount calculation has been met.
 11. A fuel cutoffcontrol device comprising: an air introducing pipe connected to anexhaust pipe of an engine; an air cut valve provided on the airintroducing pipe; and an electronic control unit that determines underpredetermined conditions whether or not the engine is in a deceleratingstate, wherein in the decelerating state, a greater amount of fuel thana normally required amount of fuel flow is supplied during apredetermined period of time after the start of deceleration and thenfuel is cut off after the predetermined period of time has elapsed. 12.The fuel cutoff control device according to claim 11, wherein when ithas been determined that the engine is not in the decelerating state, ifthe engine is regaining speed back from the decelerating state, a lessamount of fuel than normally required is supplied.
 13. The fuel cutoffcontrol device according to claim 11, wherein the predeterminedconditions include determining a time elapsed since an engine start anddetermining a cooling water temperature.
 14. The fuel cutoff controldevice according to claim 11, wherein the air cut valve opens at a highengine speed with an engine throttle opened during normal driving oracceleration to introduce secondary air.
 15. The fuel cutoff controldevice according to claim 11, wherein the air cut valve closes at a lowengine speed with an engine throttle closed during deceleration tocutoff secondary air.
 16. The fuel cutoff control device comprising: anair introducing pipe connected to an exhaust pipe of an engine; an aircut valve provided on the air introducing pipe; and means fordetermining under predetermined conditions whether or not the engine isin a decelerating state, wherein in the decelerating state, a greateramount of fuel than a normally required amount of fuel flow is suppliedduring a predetermined period of time after the start of decelerationand then fuel is cut off after the predetermined period of time haselapsed.
 17. The fuel cutoff control device according to claim 16,wherein when it has been determined that the engine is not in thedecelerating state, if the engine is regaining speed back from thedecelerating state, a less amount of fuel than normally required issupplied.
 18. The fuel cutoff control device according to claim 16,wherein the predetermined conditions include determining a time elapsedsince an engine start and determining a cooling water temperature. 19.The fuel cutoff control device according to claim 14, wherein the aircut valve opens at a high engine speed with an engine throttle openedduring normal driving or acceleration to introduce secondary air. 20.The fuel cutoff control device according to claim 16, wherein the aircut valve closes at a low engine speed with an engine throttle closedduring deceleration to cutoff secondary air.